Various types of hitch control systems have been heretofore designed, used and proposed. The purpose of each of these systems is to control the elevation of the hitch assembly thereby maintaining the ground penetration of the equipment or ground engaging assembly attached to the hitch assembly at a substantially constant depth during its operation.
Most conventional hitch control systems include simple controls for setting the depth of ground penetration by the ground penetrating equipment adapted to be attached to the hitch assembly. Known systems include a hitch command lever which sets the preferred elevational position of the hitch assembly and thereby the depth of ground penetration equipment and a "mix" control which regulates the draft load sensed by the hitch assembly and resulting from the ground interaction with the assembly being positioned by the hitch assembly. Changing soil conditions in any particular field being worked or in different fields, however, make such heretofore known systems inadequate. As will be appreciated by those skilled in the art, such known systems offered limited adjustability of the control systems to changing field conditions and, thus, complicate operations for the owner who may have thousands of acres of land with different soil characteristics throughout the various fields. Moreover, once such systems are set, there is no opportunity for the operator to make on-going changes to the hitch assembly setting in response to changing conditions in the field being worked.
Hitch assemblies are designed to work with a myriad of different ground engaging and penetrating assemblies or equipment. The limited ability to adjust the heretofore known systems, limits the ability of the system to adjust to changes associated with the assemblies or equipment attached thereto. Thus, the versatility of the implement is substantially reduced thereby increasing the cost to the farmer.
The heretofore known hitch control systems tend to vigorously respond to changes in sensed draft loads being applied to the hitch assembly. While a vigorous response may be appropriate in some circumstances, the changes to the hitch loading can result in an inconsistent ride for the operator which quickly wears on the operator throughout a day of field operations. On the other hand, the inability of the hitch control assembly to respond to changing load conditions imparted to, the hitch assembly impacts on the engine performance and wear.
Most hitch control systems are capable of operating in more than one operating state. For example, if the off-highway implement is being driven across a field with the ground engaging equipment or assembly attached thereto being adapted to either engage or penetrate the ground, the control system preferably operates the hitch assembly in a DRAFT state. On the other hand, some hitch assemblies operate satisfactorily in a POSITION state during which the hitch assembly moves between two positions. When the ground penetrating equipment is being initially connected to the hitch assembly, most hitch assemblies include remote switches to facilitate raising or lowering the hitch assembly from an area remote from the operator station of the implement. To allow for operation of the remote switches, the control system is operable in a MOMENTARY state. Alternatively, if the assembly is being transported from one location to another as by driving the implement with the assembly attached thereto, the hitch assembly is operated in a HITCH UP state.
While improvements have been made to such control systems, no known control system provides a lower limit to movement of the hitch assembly when it operates in DRAFT state. With known control systems, the hitch assembly and the equipment or assembly carried thereby are substantially free to descend to the mechanical limits of the hitch assembly. The inability to set a lower limit complicates ground penetration in that the equipment can go below the setting selected by the operator thus causing related operational problems for the off-highway implement during the DRAFT state.
Most heretofore known control systems control their descent rate of the hitch assembly to lower the equipment toward the ground from a raised position. Such systems, however, do not consider the weight of the equipment that is attached to the hitch assembly when designing the control systems. Thus, hitch assemblies having relatively large pieces of equipment connected thereto will naturally descend at a faster rate than the hitch assembly will when a smaller piece of equipment attached thereto. During operation of the remote switches, heretofore known control systems tailed to regulate the descent rate of the hitch assembly based on the weight of the equipment connected thereto. The inability to know how fast the such equipment may move toward the ground from a raised or elevated position, can cause serious and costly damage to such equipment as through operator neglect. A damaged piece of equipment can cause further downtime resulting from the repairs or replacement of parts required for the equipment.
Thus there is a need and a desire for a hitch assembly control system which addresses these significant drawbacks associated with the heretofore known control systems and provides the operator with flexibility and assurance of operation which was heretofore unknown.
As increasingly sophisticated control systems are devised, particularly control systems relying upon electronic and microprocessor control, there is also a need for calibration methods designed to enhance control performance. In particular, control by a digital signal processor is simplified and improved if certain values related to physical limits and parameters of the mechanical system, and electrical characteristics of the control system are stored in the processor during a calibration sequence for use throughout the control process. Such parameters would advantageously include the minimum current that may be supplied to solenoid coils to raise and lower the hitch, minimum and maximum hitch positions, minimum and maximum command lever positions, and the mapping of command lever positions on hitch positions.
In addition, such calibration methods are particularly useful where a control system may be installed on various vehicle models, such as within a family of tractors, or where physical or electrical variations may exist between individual machines within a single model. For example, the range of hitch movement may vary greatly between models, such as from 55 to 76 degrees of angular displacement. The range of movement of command hardware can also vary widely. Within a single model of vehicle, variations within manufacturing tolerances inevitably lead to differences between machines, requiring individual calibration of each completed vehicle.
Finally, known control systems, while affording control of certain hitch parameters, such as position or height, based upon the deviation between some command input and a sensed actual value of the parameter, generally do not compensate for changes in physical or electrical characteristics of the control system during operation. For example, upon startup of an agricultural vehicle, a cold battery and electrical system will generally furnish a lower voltage than the rated voltage. As the vehicle warms up during operation, the voltage will generally increase. Similarly, the resistance of solenoid coils in the actuator circuit may change during operation. The failure to account for such changes, and to adapt control signals accordingly can lead to inconsistent control throughout the period of operation of the vehicle. Accounting for such parameter changes entails not only measuring the parameters and calibrating the processor accordingly, but also adjusting control signals based upon changes in the parameter measurements.